Fluids, e.g., water, oil and the like, are often "conditioned" by passing them through filter cartridges to remove particulate matter. Such cartridges are typically confined within housings into which the fluid is introduced for filtering and later removed. Some installations use multiple filter cartridges within a single housing.
Example of a filter cartridge and housing are shown in U.S. Pat. Nos. 3,988,244 (Brooks) and 4,507,200 (Meissner). Such examples are of particular interest because unlike other filter cartridges mentioned below, the Brooks and Meissner cartridges use dual flow paths. That is, all fluid to be filtered is introduced through a central inlet. A portion of such fluid flows from the center area radially outward through an inner annular filter element. The remainder of the fluid flows to the outer perimeter of the cartridge and from there, radially inward through an outer annular filter element. Both flows join at an annular passage (a space between the filter elements) and pass downward through openings in the annular pocket and thence to a discharge port.
Both the Brooks and Meissner patents show the filter cartridge seated in an annular pocket having a width substantially less than that of the end cap, both dimensions being measured radially. However, the current practice used to "interface" a filter cartridge of the Brooks or Meissner type with the housing is to very snugly seat the end cap in an annular pocket of a width about equal to that of the end cap.
A snug end cap-to-pocket "fit" is used to prevent (or substantially prevent) fluid from "bypassing" the cartridge and flowing through the housing unfiltered. Of course, filtration of essentially all of the fluid passing through the filter housing is highly desirable and the known approach accomplishes that objective--but it is accompanied by a distinct disadvantage.
Such disadvantage arises from the fact that customers using filtration units with swimming pools and other high flow rate applications are demanding increased filtration capacity, i.e., filter element area, consistent with low pressure drop within a given housing. One way to provide such capacity and still maintain a relatively low pressure drop across the cartridges is to incorporate two or more filter cartridges in parallel in a common housing. U.S. Pat. No. 4,909,937 (Hoffmann et al.) shows an example of such an arrangement using concentric filters of varying size. This is a desirable arrangement since, unlike the arrangement of the Pett patent discussed below, it utilizes a relatively high percentage of the space available in the cylindrical housing.
When filters of the Brooks and Meissner type are arranged concentrically and seated in a wide annular pocket as described above, the outer cartridge is quite large if the filtration area of the unit is substantial. Therefore, the end cap-to-pocket fit requires a good deal of force to release the cartridge from the housing as when cleaning or replacing the cartridge. Filter cartridges forcibly dislodged from such pockets (as they must be) may be deformed or otherwise damaged in the process.
And the problem is often aggravated because such cartridge is soaked with fluid and is quite heavy. Lifting a large, sticking, waterlogged filter cartridge vertically upward from its housing can be a trying, rather rigorous chore. As further explained below, such cartridges may weigh 40-50 pounds when wet as compared to only 10-15 pounds when dry.
Examples of other types of filter cartridges and housings are shown and described in U.S. Pat. Nos. 4,319,997 (Pett) and 4,824,564 (Edwards et al.). The arrangement shown in the Pett patent includes a domed generally cylindrical housing having a lower compartmented region into which are threaded multiple filter cartridges. Fluid enters the housing through a central inlet. Filtered fluid passes into the compartment where it joins fluid from other filters and is exhausted through a radially-spaced tube.
The Pett arrangement anticipates fluid leakage around the filter neck and includes what is called a leakage control channel to receive and drain away leaking fluid. Such arrangement suggests that if one wishes to increase the filtration area within the housing, one simply adds additional cartridges, all of which are substantially identical to one another.
The filter shown in the Edwards et al. patent has a lower end cap including nipples extending into apertures in the housing base plate. O-ring seals between the nipples and apertures prevent fluid leakage. The single cartridge is captive in a generally cylindrical housing. Like that of the Pett patent, the Edwards et al. arrangement uses a radially-spaced outlet tube and a central inlet tube.
The housing shown in the Hoffmann et al. patent is domed and generally cylindrical. It appears the filter cartridges are simply positioned atop the connecting adapter which has one or more inlet and outlet tubes, depending upon the embodiment. The concentrically-arranged cartridges are of different diameters and appear to be individually replaceable. When doing so, the connecting adapter appears to be left in place. O-ring seals are provided between the connecting adapter and the housing base but none are apparent between the cartridges and the adapter.
An improved filter cartridge which provides substantially fluid tight sealing with its housing, which nevertheless requires relatively little effort to remove, which can be used in multiple-cartridge installations and which could be used in a "nested" or stacked arrangement would be an important advance in the art.